Pilgrims of the Irish diaspora who do a stint in the old country and then proselytise about its charms now constitute an entire subgenre of memoirist - thus raising the bar rather high when another such pilgrim comes along. Unsentimental and self-deprecating, Briton John Walsh distinguished himself from the pack in The Falling Angels. And now, as a fine stylist, Thomas Lynch rises head and shoulders above the bog of other Irish-Americans who adopt Ireland as a second home and then, with much time on their hands in lousy weather, get fired up to write about it.

Yet the formal incoherence of Booking Passage is frustrating. The flap-copy attempts to flaunt its kitchen-sink approach as a selling point, promoting the book as "part travelogue, part cultural study, part memoir and elegy, part guidebook". Why stop there? Try adding "part political diatribe, part story of the author's life back in Michigan, part poetry anthology, part long boring name-dropping diary of the author's poetry readings . . ." One is tempted to draw Lynch aside and explain to him what a book is. Yet Lynch also writes poetry, and perhaps imagines that the same broad associative license extends to prose.

Early on, he explains that he was some way into this manuscript when 9/11 led him to question - as so many Americans then at work on efforts unrelated to Islamic terrorism would also question - what he was on about. Yet after the dust settled, most savvy American writers got a grip. The world hadn't changed that much, and it was still possible to write a book about Ireland, for example. Not so Lynch, for the planes that ripped through the World Trade Center seem to have left permanent holes in his original proposal. Into these holes he has poured philosophising about nearly anything, from the gender wars to the invasion of Iraq.

As far as one can make out, Lynch's modest original concept was to write a memoir about having visited distant relatives in County Clare as a youth, and his regular visits to the country of his forebears over the span of 30 years, during which time the former European basket-case transformed itself from the land of soda bread and cabbage to a brave new world of focaccia and rocket. Had he stuck to this model, the results would have been a slight though unified book whose formal cliché was more than redeemed by astute observation and almost evangelical prose. This discipline of writing about something in particular instead of everything that has popped into the author's head in the course of a manuscript might just about have allowed the asides on Lynch's life as a Michigan funeral director, about which his observations are trenchant.

Apparently, rather than being shaped by tradition and creed, contemporary American funerals are often themed like parks, and the bereaved may choose a casket and accessories garishly appointed with totems of the deceased's favourite pastime, such as golf. Lynch's description of the "golf bag urn" is as hilarious as it is depressing. Of this new funereal formula, he writes: "Distanced from communities of faith and family, the script has changed from the essentially sacred to the essentially silly. We mistake the ridiculous for the sublime . . . Instead of Methodists or Muslims, we are golfers now; gardeners, bikers and dead bowlers . . . The dead are downsized or disappeared or turned into knick-knacks in a kind of funeral karaoke."

I told you he could write. Whether that passage belongs in a memoir about Ireland is another question.

When Lynch does write a memoir about Ireland, the results are sometimes splendid. His outrage about the sex scandals in the Roman Catholic church is fresh and stinging. The rash of priests caught with their hands in little boys' shorts "has, in the space of a decade, disestablished a church that had been rooted for centuries". He notes: "Such misconduct does not shake the faith, it kills it." Moreover, the Irish laity has found some mean satisfaction in bringing the lofty down to earth. In a nation that professes to be 90% Catholic, "Beneath the religious conformity was a current of popular contempt . . . There were, apparently, deep reserves of anger and resentment towards a clergy that had 'lorded it over' the people for far too long."

Lynch is on shakier ground regarding Northern Ireland, if he imagines declaring preachily that Ulster's conflict is not about religion but "otherness" makes a contribution to the vast library of literature on the subject. Insertions on Iraq smack of an insecure urge to be right-on. But then, ultimately the reader can always skip the irksome for the good bits. In Lynch's defence, these are numerous.

· Lionel Shriver's We Need to Talk about Kevin is published by Serpent's Tail. Order Booking Passage for £11.99 with free UK p&p on 0870 836 0875.